P. Rüegsegger (Peter)http://repub.eur.nl/ppl/18264/
List of Publicationsenhttp://repub.eur.nl/eur_signature.pnghttp://repub.eur.nl/
RePub, Erasmus University RepositoryIntroduction and evaluation of a gray-value voxel conversion techniquehttp://repub.eur.nl/pub/15366/
Sun, 01 Apr 2001 00:00:01 GMT<div>J. Homminga</div><div>R. Huiskes</div><div>R. van Rietbergen</div><div>P. Rüegsegger</div><div>H.H. Weinans</div>
In micro finite element analyses (microFEA) of cancellous bone, the 3D-imaging data that the FEA-models are based on, contain a range of gray-values. In the construction of the eventual FEA-model, these gray-values are commonly thresholded. Although thresholding is successful at small voxel sizes, at larger voxel sizes there is substantial loss of trabecular connectivity. We propose a new method: the gray-value method, where the microFEA-models use the information within the 3D-imaging data directly, without prior thresholding. Our question was twofold. First, how does the gray-value method compare to both plain and mass-compensated thresholding? Second, what is the effect of element size on the results obtained with the gray-value method? We used nine microCT-scans of human vertebral cancellous bone. These were degraded to represent different resolutions, and converted into microFEA-models using plain thresholding, mass-compensated thresholding, and the gray-value method. The apparent elastic moduli of the specimens were determined using microFEA. The different methods were compared on the basis of the apparent elastic moduli, compared to those calculated for a 28 microm reference model. The results showed that the gray-value method greatly improves the results relative to other methods. The gray-value method gives accurate predictions of the apparent elastic moduli, for voxel sizes up to one trabecular thickness (Tb.Th.). For voxel sizes greater than one Tb.Th. the accuracy, although still better than for both thresholding methods, becomes increasingly worse.Bone density reduction in various measurement sites in men and women with osteoporotic fractures of spine and hip: The European quantitation of osteoporosis studyhttp://repub.eur.nl/pub/67979/
Wed, 10 Mar 1999 00:00:01 GMT<div>N. Kröger</div><div>M. Lunt</div><div>J. Reeve</div><div>J. Dequeker</div><div>J. Adams</div><div>J.C. Birkenhäger</div><div>M. Diaz Curiel</div><div>D. Felsenberg</div><div>L. Hyldstrup</div><div>P. Kotzki</div><div>A.-M. Laval-Jeantet</div><div>P. Lips</div><div>E. Louis</div><div>R. Perez Cano</div><div>C. Reiners</div><div>J.G. Ribot</div><div>P. Rüegsegger</div><div>P. Schneider</div><div>P. Braillon</div><div>J. Pearson</div>
Finite element analysis of trabecular bone structure: a comparison of image-based meshing techniqueshttp://repub.eur.nl/pub/15362/
Tue, 01 Dec 1998 00:00:01 GMT<div>D. Ulrich</div><div>R. van Rietbergen</div><div>H.H. Weinans</div><div>P. Rüegsegger</div>
In this study, we investigate if finite element (FE) analyses of human trabecular bone architecture based on 168 microm images can provide relevant information about the bone mechanical characteristics. Three human trabecular bone samples, one taken from the femoral head, one from the iliac crest, and one from the lumbar spine, were imaged with micro-computed tomography (micro-CT) using a 28 microm resolution. After reconstruction the resolution was coarsened to 168 microm. First, all reconstructions were thresholded and directly converted to FE-models built of hexahedral elements. For the coarser resolutions of two samples, this resulted in a loss of trabecular connections and a subsequent loss of stiffness. To reduce this effect, a tetrahedral element meshing based on the marching cubes algorithm, as well as a modified hexahedron meshing, which thresholds the image such that load carrying bone mass is preserved, were employed. For each sample elastic moduli and tissue Von Mises stresses of the three different 168 microm models were compared to those from the hexahedron 28 microm model. For one sample the hexahedron meshing at 168 microm produced excellent results. For the other two samples the results obtained from the hexahedral models at 168 microm resolution were poor. Considerably better results were attained for these samples when using the mass-compensated or tetrahedron meshing techniques. We conclude that the accuracy of the FE-models at 168 microm strongly depends on the bone morphology, in particular its trabecular thickness. A substantial loss of trabecular connections during the hexahedron meshing process indicates that poor FE results will be obtained. In this case the tetrahedron or mass-compensated hexahedron meshing techniques can reduce the loss of connections and produce better results than the plain hexahedron meshing techniques.European semi-anthropomorphic spine phantom for the calibration of bone densitometers: Assessment of precision, stability and accuracy the European quantitation of osteoporosis study grouphttp://repub.eur.nl/pub/72411/
Mon, 01 May 1995 00:00:01 GMT<div>J. Pearson</div><div>J. Dequeker</div><div>J.M. Henley</div><div>J. Bright</div><div>J. Reeve</div><div>W.A. Kalender</div><div>A.-M. Laval-Jeantet</div><div>P. Rüegsegger</div><div>D. Felsenberg</div><div>J. Adams</div><div>J.C. Birkenhäger</div><div>P. Braillon</div><div>R.E. Curiel</div><div>M. Fischer</div><div>F. Galan</div><div>P.P. Geusens</div><div>L. Hyldstrup</div><div>P. Jaeger</div><div>R. Jonson</div><div>J. Kalef-Ezras</div><div>P. Kotzki</div><div>N. Kröger</div><div>A. van Lingen</div><div>S. Nilsson</div><div>M. Osteaux</div><div>S.C. Cano</div><div>D.M. Reid</div><div>C. Reiners</div><div>J.G. Ribot</div><div>P. Schneider</div><div>D.O. Slosman</div><div>G. Wittenberg</div>
Up to now it has not been possible to reliably cross-calibrate dual-energy X-ray absorptiometry (DXA) densitometry equipment made by different manufacturers so that a measurement made on an individual subject can be expressed in the units used with a different type of machine. Manufacturers have adopted various procedures for edge detection and calibration, producing various normal ranges which are specific to each individual manufacturer's brand of machine. In this study we have used the recently described European Spine Phantom (ESP, prototype version), which contains three semi-anthropomorphic "vertebrae" of different densities made of simulated cortical and trabecular bone, to calibrate a range of DXA densitometers and quantitative computed tomography (QCT) equipment used in the measurement of trabecular bone density of the lumbar vertebrae. Three brands of QCT equipment and three brands of DXA equipment were assessed. Repeat measurements were made to assess machine stability. With the large majority of machines which proved stable, mean values were obtained for the measured low, medium and high density vertebrae respectively. In the case of the QCT equipment these means were for the trabecular bone density, and in the case of the DXA equipment for vertebral body bone density in the posteroanterior projection. All DXA machines overestimated the projected area of the vertebral bodies by incorporating variable amounts of transverse process. In general, the QCT equipment gave measured values which were close to the specified values for trabecular density, but there were substantial differences from the specified values in the results provided by the three DXA brands. For the QCT and Norland DXA machines (posteroanterior view), the relationships between specified densities and observed densities were found to be linear, whereas for the other DXA equipment (posteroanterior view), slightly curvilinear, exponential fits were found to be necessary to fit the plots of observed versus specified densities. From these plots, individual calibration equations were derived for each machine studied. For optimal cross-calibration, it was found to be necessary to use an individual calibration equation for each machine. This study has shown that it is possible to cross-calibrate DXA as well as QCT equipment for the measurement of axial bone density. This will be of considerable benefit for large-scale epidemiological studies as well as for multi-site clinical studies depending on bone densitometry.